This non-provisional application claims priority under 35 U.S.C. §119(a) on patent application Ser. No. 1,020,682 filed in The Netherlands on May 27, 2002, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to an ink composition which is solid at room temperature and liquid at elevated temperature, said ink composition containing a resin and being suitable for use in an inkjet printer.
2. Related Art
It is known to use resins in relatively large quantities in meltable ink compositions (hot melt inks) for inkjet printers. Inks of this kind are solid at room temperature and melt at elevated temperature. Typical melting points are in the range of 60 to 120° C. The melted inks are jetted at a temperature at which they are thinly viscous, typically 100 to 160° C., by means of an inkjet printer as adequately known from the prior art. Resins enable the ink to be sufficiently tough after cooling so that the ink is more resistant to mechanical loads on the printed receiving material, such as gumming, scratching and folding. Although crystalline materials are generally harder, they are also much more brittle, so that printed matter made using a mainly crystalline ink composition is fairly sensitive to damage. The use of resins in ink compositions also has the advantage that dyes can be dissolved relatively well therein and pigments can be dispersed relatively easily therein. In addition, resins have the advantage that after solidification they are often transparent so that it is possible to make color prints using subtractive color mixing. The disadvantage of resins is that generally they are relatively viscous, even after they have been softened at high temperature, and cannot therefore be used in large quantities in hot melt inks.
Amorphously solidifying monomeric resins are known from U.S. Pat. No. 6,071,986. Resins of this kind, which solidify completely amorphously, have the advantage that they are not very viscous, because of their relatively low molecular weight. The disadvantage of these resins, however, is that their amorphous state is not sufficiently stable. As a result, these resins will also crystallise after a shorter or longer period. Even if these known resins are used in an ink composition, there will be some post-crystallization of the resins. This in turn has the result that the quality of a printed image, i.e. after the corresponding ink has solidified on the receiving material, will deteriorate in the course of time.
Esters of 2,2′-biphenol and aromatic acids are known from EP 0 978 548. These are also examples of monomeric amorphously solidifying resins. However, these resins still appear to have some tendency to post-crystallization so that the properties of the solidified ink change in the course of time, particularly when printed receiving materials are stored under extreme conditions, for example at relatively high temperatures.